Electrical coupling circuits



Ap il 21, 1942. p. CQLCHESTER Em 2 280,282

ELECTR ICAL COUPLING CIRCUITS Filed'Nov. 5, 1940 2 Sheets-Sheet l l l awamaiazififffi w I BY ATTORNEY pril 21, 1942.

c. D. COLCHESTER ETAL ELECTRICAL COUPLING CIRCUITS 2 Sheets-Sheet 2 Filed Nov. 5, 1940 o m 0 0 T R r d 5. 2 C A z Ez 1 2 w 2 f m FM if a n K m r w 1 n F J QJJ GWDIbdI P n I. I I I I. I a Y L {L I! I? 4 u I L! Iatented Apr. 21, 1942 -UN TED STATES PATENT O'FFlCE ELECTRICAL COUPLING CIRCUITS Christopher Dering Colchester, Sanderstead, and Arthur Tisso Starr, Chelmsiord, England, assignors. to Radio Corporationof America, a corporation of Delaware ApplicationNovember5, 1940, Serial No.

In Great Britain August 31, 1939 8 Claims. (01. 17844) sponding other conductor 01' the other said input circuit,and a resistance connected between said other conductor and the said corresponding one conductor, one conductor of the output circuit being connected to said one conductor of impedance elements; Fig. 9 shows the reactance curves for elements Z and of Fig. 1, Fig. 10 shows the circuit of Fig. 1, z and being replaced respectively by the networks of Figs. 2 and 3; Fig. 11 shows the circuit of Fig. 1, Z and 7 being replaced respectively by the networks 01' Figs. 4 and 5; and Fig. 12 shows a circuit of the form of Fig. 1 but for coupling four input cirsald one input circuit andthe other conductor Quits to a common Output Circuit Z and of the output circuit being connected to the said 2 R: corresponding other conductor of said other in- 7 put circuit, and wherein said first mentioned impedance network presentsa highimped-ance to currents of the frequency oi said one input circuit and alow impedance to currents of the frequency of said other input circuit and said second impedance network presents a high impedance to currents of the frequency oisaid second input and a low impedance to currents of the frequency of said one input circuit. The said resistance should preferably be equal to the impedance oithe output termination.

Where it is desired to couple more thantwo input circuits to a common output circuit, the input circuits may be coupled to pairs in the manner above set forth, and the outputs of the several coupled pairs again coupled.

The invention is illustrated in the accompanybeing replaced respectively by the networks of Figs. '7 and 8.

In Fig. 1, the symbols I1 and I: represent the two input circuits and 0 represents the common output circuit. Z and p 7, represent the two impedance networks. The impedance 01 Z should, ideally, :be infinite at the frequency. v V

shouldbe zero at the frequency ing drawings wherein Fig. 1 shows the general 40' v 5; gligcgtliigcsi 2 and 3 show the forms which neto input circuit I2. The impedance of Fig. 1 may take; Figs. ifications of Figs. 2 and 3 to overcome the effect of dissipation in the resistive components of L1. L2 and In; Fig. 6 shows the manner of coupling together more than two input circuits to a common output circuit; Figs. 7 and 8 show modified 4 and 5 illustrate mod-.

, should, ideally, be infinite at the frequency of input circuit Ia,- and should be zero at the irequency of input circuit I1. Rrepresents a resistance connecting the input ends of Z and Thesimplest form of Z is that in which Z is zero when w is zero or has the value of m, and is infinite when or has the value of an or is infinite as illustrated in Fig. 9 which shows the reactance curves for Z (full line) and (broken line).

The network Z may take the form, shown in Fig. 2, of an inductance L1 shunted by a condenser C3, the whole being in series with a further inductance L2. The inverse network may take the form, shown in Fig. 3, of an inductance La in series with a condenser 01, the whole being shunted by a condenser C2. This is shown in Fig. .10.

The impedance of the network Z is given by L L C If, as stated, the frequency of input circuit I1 jw(Li+L:)( 2

It will be seen that there are two relations in Equations 1 to. determine the three unknown quantities L1, L2, Ca. A third relation is arbitrary, and the best choice is given by making the loss curves in the neighborhood of. ml and (02 of the same shape. If 01 is the transfer constant from input I to the output and 02 from and ' input 2 tothe output then and To obtain the same shape for the loss curves, it is necessary that a it 2.2

dwz w dwR w;

This gives L1+L.= f -44) Thus, for network Z Equations 1 and 4 give steeply beyond (02.

the pair I3 and I4 may then be between m3 and on and for the inverse network Equations 1 and 4 give and across condensers C1 and C2 in network high resistances and respectively. The circuit when thus modified is shown in Fig. 11.

Where it is desired to couple four input circuits of frequencies a a 21r and 27 (these being in order of magnitude), to a common output circuit, this may be effected as illustrated in Fig. 6, by combining inputs I1 and I2, and I3 and I4 respectively, and then combining the pairs. In this case the best pass frequency of the pair 11 and 12 may be between an and (02, preferably nearer to wz since the attenuation rises more The best pass frequency of The networks will be of the form described above in connection with Figs. 2 to 5. Similar conditions apply to combining the pairs. In this case the best pass frequency of the pair Ii. and I2 may be between (01 and ma, preferably nearer to an since the attenuation rises more steeply beyond wz. The best pass frequency of the pair I: and I4 may then be between an and an. The networks will be of the form described above in connection with Figs. 2 to 5. Similar conditions apply to the inputs I3 and 14. The corresponding loss curves are shown in Fig. 9.

It is preferred, however, to group alternative channels in pairs such that the impedance Z of the drawing has, in this case, to be infinite at w]. and (v3 and zero at m and (04. In this case the network Z may take the form, shown in Fig. 7,

of an inductance La shunted by a condenser Cs, and'inductance La shunted by a condenser 04 and an inductance Ill, these three elements being connected in series. The inverse network may take the form, shown in Fig. 8, of an inductance Ll in series with a condenser C2, an inductance L5 in series with a condenser C3 and a condenser C1 these three elements being connected in parallel. The circuit according to this modification is shown in Fig. 12.- The values of the several inductances and condensers are-given wiM-wi im i) whiz] The invention is susceptible of various modifications; thus for example the impedance networks Z and is equal to R (R. being the value of the resistance connected to the two impedances and being equal to the output impedance) gives best results, matters may be so arranged that R is equal to the productof R and of the impedance of the output circuit.

, What-is claimed is:

1. A coupling circuit for coupling two alte'rnating current input circuits of different frequencies to a common output circuit, comprising an impedance network connected between one conductor of one input circuit and the corresponding one conductor of the other input circuit, a second impedance network connected between the other conductor of said one input circuit and the corresponding other conductor of the other aid input other conductor and the said v corresponding one conductor, one'conductor of" the output circuit I being connected saidone conductor of said one input circuit, the other conductor of the output circuit being connected to the said corresponding other conductor of said other input circuit, said first mentioned impedance network being comprised of an inductance shunted by a condenser, the .whole being in series with a further inductance and presenting a high impedance tocurrents of the frequency of said one input circuit and a low impedance to currents of the frequency of said other input circuit, said second impedance network being comprised of an inductance in series with a condenser, the whole being shunted by a condenser and having a'high impedance to currents of the frequency of said second input and a low impedance to currents of said one input circuit.

' 2. A1coupling circuit for coupling two alternating currentinput circuits of diiferent frequencies to a common output circuit, comprising a first impedance network, a resistance and a seca 0nd impedance network serially connected in the order named between the two'conductors of the output circuit, the series connection of one of the impedance networks and the resistance being connected between the terminals of one'input circuit, the series connection of the other of said impedance networks and the resistance being connected between the terminalsofthe other input circuit, said networks each consisting of inductance and capacitance and each presenting a high'impedance to currents of the frequency of the input circuit between it is connected and a of the frequency of th terminals of which it is low impedance to currents input circuit between the not connected.

3. A coupling circuit for coupling two alternating current input circuits of frequency an and m respectively to a, common output circuit, comprising a first impedance network, a resistance and a second impedance network serially connected in the order named between the two conductors ofihe output circuit, the conductors of the input circuit of frequency on being connected across the series connection of the first impedance network and the resistance, the conductors of the input circuit of frequency or: being connected across the series connection of the second impedance network and the resistance, said networks each consisting of inductance and capacitance, the first presenting a high impedance to currents of frequency s1 and a low impedance to currents of frequency we and the second presenting a high impedance to currents of frequency w: and a low impedance to currents of frequency ml.

4. A coupling circuit according to the invention defined in claim 3 wherein the first impedance network comprises a pair of inductances in series and a capacity in shunt to one of them,

and the second impedance network comprises the series connection of an inductance and a capacity and a capacity inshunt to said series connection.

5. A coupling circuit according to the invention defined in claim 3 wherein the first impedance network comprises a pair of inductances L1 and L2 in series and a capacity C: in shunt to inductance L1, and the second impedance network comprises the series connection of an inductance L3 anda capacity C1 and a capacity C2 n shunt to said se i s connection, the values of circuit, and a resistance connected between said A of the frequency the terminals of which said inductances and capacities being determined by the following expressions:

1 l 2 Ron R 1 "172 E'R R. being the value of the resistance serially connecting the impedance networks.

6. A coupling circuit according to the invention defined in claim 3 wherein the first impedance network comprises a pair of inductances in series and a capacity inv shunt to one of them, and the second impedance network comprises the series connection of an inductance and a capacity and a capacity in shunt to said series connection, and a resistance connected across each of the condensers in said impedance networks.

7. A coupling circuit according to the invention defined in claim 3 wherein the first impedance network comprises a pair of inductances L1 and L2 in series and a capacity C3 in shunt to inductance L1, and the second impedance network comprises the series connection of an inductance In and a capacity C1 and a capacity C2 in shunt to said series connection, and a resistance connected across each of the condensers C1, Ca and C3, the values or the resistances connected across the condensers C1, C2 and Ca being equal respectively to i 3. 2 R19 2 an 3 where R1, R2 and R: are respectively the values of the resistive components of the inductances L1, L2 and La and R is the value of the resistance serially connecting the impedance networks.

8. A coupling circuit for coupling four alternating current input circuits of frequency m, we, to: and we respectively to a. common output circuit, comprising, a first impedance network, a resistance and a second impedance network serially connected in the order named between the two conductors of the output circuit, the conductors of the input circuits of frequencies or and us bein connected across the series connection of the first impedance network and the resistance, the conductors of the input circuits of frequencies w: and at being connected across the series connection of the second impedance network and the resistance, the first impedance network comprising three inductances in series and a capacity individually connected in shunt to two of them, and the second impedance network comprising the parallel connection of a capacity and two paths each consisting of a series connection of an inductance and a capacity.

CHRISTOPHER DERING COLCHESTER. ARTHUR TISSO STARR. 

